The present invention is directed to a lock nut and, more particularly, to a lock nut that is substantially free running when screwed onto a male threaded member and has a breakaway torque which is a relatively high percentage of the applied locking torque. The lock nut of the present invention provides a two-way locking action by biting and spreading into a confronting surface and by deforming in response to reaction force applied first at the thinned corners and later at the edge perimeter of the bearing end face to bear radially against the male threaded member locking thereto.
A primary design consideration for most if not all lock nuts is to make certain that the lock nut resists loosening until a suitable breakaway torque is applied. There are of course many different known types of lock nuts. One known type of lock is a spring nut formed of a relatively thin stamping usually with only one and a fraction thread, which has the disadvantage of a very low locking torque and a correspondingly small breakaway torque. Also, in U.S. Pat. No. 1,734,445 there is disclosed a related prior art lock nut which has radial saw cuts across each pair of wrenching side faces defining plural sector-like portions or castellations, and at the opposite or bearing end face of the lock nut directed toward a confronting surface against which the lock nut is to be tightened, the lock nut has a dished portion to define a continuous circular fulcrum. As the lock nut is tightened on a bolt to engagement with a confronting surface, the reaction force applied by the latter to the circular fulcrum causes the castellations to bear radially inward tightly gripping the shank of the bolt to lock thereto.
Another spring-type lock nut is shown in U.S. Pat. No. 2,016,610 and has an arch-like profile so that upon tightening the lock nut on a bolt to engagement with a confronting surface, the reaction force from the latter creates a spring pressure in the opposed ends of the arch deforming the lock nut which pinches the bolt to lock thereto. U.S. Pat. Nos. 2,495,409 and 2,546,332 show still other lock nuts which have a continuous annular groove in the side faces thereof concentric about the bore so that upon tightening the lock nuts on a bolt against a confronting surface the groove facilitates deforming of part of the lock nut body so that the female threads in the bore distort and frictionally lock to the male threads on the bolt.